Contactless relay

ABSTRACT

A contact free relay having an electromagnetic control circuit and one or more electronic switching circuits disposed in the magnetic field of the electromagnetic control circuit, wherein the contact free elements are controlled by the magnetic field. The contact free elements are magnetic responsive resistors connected to one or more controllable semiconductors and mounted within the exciting coil field between one or more ferromagnetic yoke plates.

United States Patent Appl No.: 77,848

Foreign Application Priority Data Schmitt 1451 May 2, 1972' CONTACTLESS RELAY References Cited [72] Inventor: Karl Schmitt, Achern, Germany UNITED STATES PATENTS [7 3] Assignee: Gehap Gesellschait Handel and Patentverv g g i t 'l rt G & C A h G J a lflll e a m m c em er 3,315,204 4/1967 Weiss ..338/32 3,569,895 3/1971 Fujisada... ..338/32- Filed? 1970 3,553,498 l/l97l Yamada ..307/299 Primary Examiner-Donald D. Forrer Assistant E.\'aminerB. P. Davis Art0rne vAllison C. Collard ABSTRACT A contact free relay having an electromagnetic control circuit and one or more electronic switching circuits disposed in the magnetic field. of the electromagnetic control circuit, wherein the contact free elements are controlled by the magnetic field. The contact free elements are magnetic responsive resistors .connected to one or more controllable semiconductors and mounted within the exciting coil field between one or more ferromagnetic yoke plates.

11 Claims, 19 Drawing Figures PATENTEDMAY 21972 3. 660,695

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KARL SCHMITT lat 1; orne PATENTEUMAY 21972 3,660,695

SHEET u 0F 5 lm'e/llor KARL SCHP I'L'T LL WQ- Q Attorney PATENTEDMAY 2 I912 SHEET 5 BF 5 CONTACTLESS RELAY by the magnetic field, consists substantially of a magnet field dependent resistor, which is connectedwith a power supply through a pre-resistor. The magnet field dependent resistor is connected to a transistor switching arrangement which triggers the switching operation, depending on=the position of the magnetic field or the voltage. The advantage is that the switching circuit is separatedgalvanically from the control circuit, without using electrical contacts.

By using a contact free relay, all disadvantages are avoided which are usually apparent when usingmechanical contacts.

Furthermore, the contact free relay operates at a much higher switching frequency, since no mechanical parts have to be moved. The control circuit is separated galvanically like in commonly known relays. The required voltage source for the switching circuit is not disadvantageous, since a special voltage is still required when using a conventional relay, in order to create the magnetic field.

Practice has shown that with-the above-described conventional relays, relatively high energies are required in order to trigger the switching operation. The present invention provides an improvement over the above-described relays since a higher sensitivity. of the total exciting circuit, and a higher switching frequencyare obtained. Furthermore, the switching arrangement is simplified by using a magnetic sensitive transistor,asocalledMagnistor.

.ments are mounted within the range of a magnetic field of the electromagnetic control circuit; The contact free elements are controlled by the magnetic field. The contact free elements in thisinvention are, for example, magnet field dependent resistors. These elements are-one or a plurality of magnet field dependent resistors within the exciting field coil with one or a plurality of soft magnetic bodies, such as, for example, yoke plates. Y I

By providing the magnet field dependent resistors with a plurality of relatively thin, longitudinally extending yoke plates within the exciting field coil, various advantages are obtained. First of all, the construction of such an arrangement is simple and inexpensive. Furthermore, a'greater sensitivity for the total exciting field circuit is obtained, as well as a higher switching frequency, because of the relatively small iron mass of the yoke plates. Moreover, the magnetic field dependent resistors have low body heat, and therefore, are independent from temperature variations. Finally, it should be noted that substantially less space is needed for the exciting and control unit of the relay, in contrast to relay coils with massive cores and closed U-shaped yokes.

It is, therefore, an objectaccording to the present invention to provide a contact free relay disposed in a magnetic field which is capable of trouble free high speed operation.

It is another object according to the present invention to provide-a contactless relay which is simple in design, easy to manufacture and reliable in operation.

Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings which more clearly disclose the many embodiments of the invention.

It is to be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.

In the drawings, wherein similar reference characters denote similar elements throughout the several views:

FIG. 1 is a cross-sectional view of the arrangement of the magnetic field dependent resistors within theexciting coil of the contact free relay; 1

FIG. la shows the arrangement of the magnetic field dependent resistors within the exciting coil of FIG. 1;

FIGS. 2 and 3 show furtherarrangements of magnetic field dependent resistors with the associated ferromagnetic yoke plates in cross section;

FIG. 4 is a plan view of the arrangement of FIG. 3;

FIG. 5 shows a further embodiment of the invention,

wherein two magnetic field dependent resistors are arranged side by side on widened yoke plates;

FIGS. 6 and 7 show in cross-sectional plan view, one embodiment, wherein the semiconductor of the magnetic field dependent resistor is on both'sides of the yoke plate;

FIGS; 8 and 9 show. further embodiments of the'embodiments of FIGS. 6 and 7; v

FIG. 10 shows a preferred switch arrangement for a contact free relay according to the invention;

FIG. 11 shows the switching a'rrangementof a magnetic sensitive field transistor;

FIG. 12 shows one switch arrangement for a contact free relay according to the invention; I

FIG. 13 shows a further embodiment of a-switching arrangement according to the invention;

FIG. 14 shows a magnetic switch with a permanentmagnet;

FIGS. 15, 16 and 17 show different arrangements for electromagnetic switches; and

FIG. 18 is a cross-sectional view through a relay coil with an associated magnetic field dependent resistor within the housing' of the relay coil; i

In FIG. 1, an exciting field coil 1 of a contact free relay is shown incross-sectional view. The exciting field coil carries two current junctions. Two resistors 4 and 5, which are dependent from a magnetic field, are provided in. the inner airspace of exciting field coil 1, which is formed in this embodiment by a plastic body3. The magnetic field dependent resistors 4' and 5 carry connections 6 and 7 which are connected withthe corresponding switch elements of the subsequent switch circuit. Magnetic field dependent resistors 4 and 5 are positioned between the end ranges of two overlapping ferromagnetic yoke plates 8 and 9, andare separated from each other by an intermediate isolator 10. The ferromagnetic yokeplates 8 and 9 run from the center, in opposite directions, to approximately the end of the coil.

In FIG. la, the arrangement of the magnetic field dependent resistors 4 and 5 are shown in an enlarged detailed drawing. As can be seen from that drawing, the magnet field dependent resistors 4 and 5 consist of each two s'emiconduct'orlayers 4 and 5' and two metal layers 4 and 5.

In FIG. 2, one arrangement of the magnetic field dependent resistors is shown, wherein two further magnetic field dependent resistors 11 and 12 are located atthe outermost face of the ferromagnetic yoke plate 9 Resistors 11 and 12 are covered by a further ferromagnetic yoke plate 13 which runs in the same direction as ferromagnetic yoke plate 8.

In FIG. 3, one arrangement is shown in which a plurality of magnetic field dependent resistors 4, 5, l1, and 12 are mounted between ferromagnetic yoke plates 8, 13, 15, and 9., 14, respectively, which run alternating opposing directions. FIG. 4 is a plan view of the arrangement shown in FIG. 3. In FIG. 5, another embodiment is shown, wherein two magnetic field dependent resistors 4'and 4a are arranged side by side between widened yoke plates 9, l4, and 8, 13, 15, respectively. The magnetic field dependent resistors can then be arranged in a superimposed manner as shown in FIG. 3.

In the same embodiments shown in FIGS. 6 and 7, a yoke plate 16 is provided which has a recess in one end range, whereby the semiconductors of the magnetic field dependent resistors 17 and 18 are arranged at both sides of the yoke plate. In other words, the magnetic conducting sensitive faces of the construction elements are mounted directly. This view is a simplification of the arrangement.

In the embodiment shown in FIG. 8, the semiconductors for the magnetic field dependent resistors 17 and 18, and 19 and 20, respectively, are directly mounted on the yoke plate at the two end ranges of the yoke.

FIG. 9 shows, in plan view, an alternate embodiment of FIG. 8, whereby the magnetic field dependent resistors are mounted side by side on a widened yoke plate.

In FIG. 10, a switch arrangement for a contact free relay is shown in accordance with the invention. The magnetic field dependent resistor 4 is located within exciting field coil 1, shown together with its connections 2. For purposes of clarification, the resistor has been drawn next to field coil 1. A condenser Cl is connected parallel with respect to the magnetic field dependent resistor 4, in order to attenuate unwanted oscilations, which would be noticeable in the form of distortions in the switch-on and switch-off regions, when high frequencies are involved. A series of integrated switch circuits 1C are connected in series and parallel at the junction with the magnetic field dependent resistor 4 and with the control resistor R which in turn is connected to the power source. The low tension side of the integrated switch circuits 1C are connected with the bases of switching transistors T1, T2, T3 and T4 via resistors R1, R2, R3 and R4. Resistors Rl-R4 are regulated in such a manner that if a short occurs, transistors T1 to T4 are not overdriven, that is, their maximum current limits are not exceeded. Switch transistors T1-T4 are thus protected in the circuit. The Zener diode ZD, which ispositioned in the voltage feedline for the integrated switch circuits 1C, serves to limit the voltage. Depending in which position the switch circuit is in, that is, which value the magnetic field dependent resistor 4 shows, transistors T1-T4 are opened or closed. In this way, they effect the contact free opening or closing of the corresponding switch circuit. By using integrated switching or wiring IC," it is possible to control at least two switch-over circuits with one field plate. Furthermore, the immediate connecting through capability by the integrated switching circuits works much more efficiently when reaching a threshold value of more than 1 KHZ, than with contact free relays in which transistors are used exclusively. In accordance with the invention, perfect square pulses of up to 20 KHZ can be obtained.

In further improvements in accordance with the subject invention, a transistor may be used which is magnetic sensitive, instead of the aforedescribed magnetic field dependent resistor. Such a transistor is known under the name of Magnistor.

As can be seen from FIG. 11, the magnetic sensitive transistor T consists of a base B, an emitter E as well as two collectors K1 and K2. These collectors are arranged symmetrically with respect to the emitter and the base. In the rest position, the collectors, the emitter and the base draw the same current without the magnetic field. An even flow of current flows in load resistors RL] and RL2, while no potential difference appears at the collectors. However, if a magnetic field is exerted on the magnetic sensitive transistor T,,,, the current flows are deflected in the transistor, similar to a halltype generator or in a field plate, that is, as in a magnetic field dependent resistor. Thus, one of the collector currents, increases while the other decreases. An analytical potential difference is created between the collectors which are linearly dependent upon the magnitude of the applied magnetic field force. This potential difference is expressed as the difference E -E The base voltage is B and the emitter current is I In principle, FIG. 12 shows a switching arrangement wherein the magnet sensitive transistor T,, is positioned in the range of the magnet coil R; of a relay coil. Thereby, the magnet sensitive transistor T,, may be mounted within the coil symmetrically between two yoke plates or outside of the coil, for instance, in the air space of a closed magnet yoke.

' In the embodiment shown, the control voltage U is at the entrance terminal of the relay coil R The base of the magnetic sensitive transistor T,, is in the center of a voltage distributor R and R which is connected to the power current and can be adjustable, if so desired. The two collectors of the magnet sensitive transistor are connected to the power supply by two outside resistors R 1 and R The emitter of transistor T,, is connected at the other end of the power supply. One of the collectors is connected to the base of a switch transistor T, via a resistor R The collector of this switch transistor is connected to load resistor R, The other terminal of resistor R connects to the power supply.

The function of the switching is as follows:

In the normal position, that is, when relay coil R is not excited, no magnetic field is exerted on the magnetic sensitive transistor T,,,. The base current is constant due to the rigidly adjusted resistors R, and R In this case, no potential difference exists across both collectors. Hence, the transistor T is open. At this point, a control voltage U is admitted to relay coil R which creates a magnetic field which is applied to magnetic sensitive transistor T Thus, one of the collector currents increases, while the other decreases. The base voltage of switch transistor T thus changes, and the transistor conducts, to switch on load resistor R,

A further switching arrangement is shown in FIG. 13, wherein the second collector is also connected with a further switching transistor T 2 by means of aresistor R The function of this switching arrangement is basically similar to the one described with respect to FIG. 2, with the exception that with magnetic sensitive transistor T,,,, two switching circuits can be modulated. The switching arrangement can be set up such that there are possibilities for changing over the switching.

In principle, a magnetic sensitive transistor T, is shown in FIG. 14, wherein a permanent magnet M can be moved towards or away from the transistor T,, in the direction of both sets of double arrows. Due to the mechanical movement of the permanent magnet, the magnetic sensitive transistor serves as a control element for a further switching circuit, whereby the whole switching arrangement operates as a magnetic switch.

In FIG. 15, the magnetic sensitive transistor T,, is located in the air gap of a U-shaped J, which is mounted within a control coil S. When coil S is energized by a control voltage U the magnetic field of the coil is exerted through the U-shaped yoke andthe magnetic sensitive transistor T,,,. The function of the switching arrangement is the same as described, above. I

In FIG. 16, one embodiment is shown, wherein a ferromagnetic core I, is provided within -a cylindrically-shaped electromagnetic coil 8 At both sides of the coil, two magnetic sensitive transistors T,, are provided, which trigger the abovedescribed function and operation of the switching arrange.

ment, after the magnetic field has been released.

In FIG. 17, two. magnetic sensitive transistors T,,, are mounted in the air gap space of a three-part separated yoke J 2 which is surrounded by a further coil S Naturally, other embodiments are possible, wherein the magnetic sensitive transistor is disposed in the range of the magnetic field of an electromagnet or permanent magnet which triggers the switching operation. In a further embodiment of the invention, it should be noted that the sensitivity of the relays can be increased when the magnetic field dependent resistor is mounted within the coil and in the air gap of a yoke which is made of a highly permeable material so that the angle between the coil axis and a plane of the magnetic field dependent resistor is between 40-90.

In accordance with FIG. 18, a coil 21 is shown .on which winding 22 is mounted. A core 23, made of a highly permeable or ferrite material, is mounted within coil body 21. Core 23 is provided with an oblique air space 24, the deflection angle of which is 40 or more with respect to the axis of the coil axis In the extreme case, this space 24' shown in dotted line, can have an angle of 90. Magnetic field depending resistor 25 is mounted in the air space of core 23 and feed lines 26 are connected to the switching circuit, as described above.

In accordance with the inventive arrangement of a magnetic field dependent resistor 25, very high switching frequencies can be obtained with the contact free relay. This is because the magnetic field lines in air space 24 penetrate magnetic field depending resistor 25 vertically, or almost vertically.

netic yoke plates, disposed substantially in the center of the magnetic field, and coupled to the switching circuit; and

atleast two magnetic field dependent resistors, having an intermediate isolation layer, disposed between said pair of overlapping yoke plates.

2. In a contact free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising:

a first ferromagnetic yoke plate, extending longitudinally in one direction, and disposed within the magnetic field; second and third yoke plates, overlapping said first yoke plate on each side, extending in an opposite direction,

and disposed within the magnetic field;

Y a first pair of magnetic field dependent resistors, disposed between said first yoke plate and said second yoke plate; and

a second pair of magnetic field dependent resistors,

" disposed between said first yoke plate and said third yoke plate.

3. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising:

a first pair of spaced-apart, overlapping ferromagnetic yoke plates, extending in one direction, disposed in the magnetic field; j

a second pair offerromagnetic yoke plates, alternately interdisposed with respect to said first pair of ferromagnetic plates, and extending in an opposite direction, disposed in the magnetic field; and

a plurality of individual magnetic field dependent resistors,

each disposed between said overlapping yoke plates.

4. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising:

a plurality of spaced-apart, overlapping magnetic field dependent resistors disposed within the magnetic field; and

a plurality of ferromagnetic yoke plates, disposed between said overlapping resistors, overlapping each other, and extending from the center of the magnetic field in alternating, opposite directions.

5. The contact free relay as recited in claim 4, comprising an additional plurality of corresponding pairs of magnetic field dependent resistors mounted side by side with respect to said ferromagnetic yoke plates, the width of said plates being expanded to accommodate said additional resistors.

6. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising:

a magnetic field dependent resistor, disposed within the magnetic field;

ferromagnetic means, disposed within the magnetic field, on

which said magnetic field resistor is disposed;

a condenser, coupled across said magnetic field dependent resistor;

a power supply;

a variable resistor, coupled to the output of said power supply and to said magnetic field dependent resistor;

a plurality of integrated, switching circuits coupled to said magnetic field dependent resistor;

limit resistors, coupled to the output of said integrated switching circuits; and

. a plurality of switching transistors, coupled to the output of said limit' resistors.

7. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising:

at least one magnetic sensitive transistor, having two collector terminals, controlled by the magnetic field of the electromagnetic control circuit;

an adjustable voltage divider, coupled to the base of said magnetic sensitive transistor;

a first resistor, coupled to 'each of said magnetic transistor collectors, for coupling power to said magnetic transistor;

a second resistor, coupled to one of said collectors of said magnetic transistors; i

at least one switching transistor, having its base coupled in v series to said second resistor; and v a load resistor, coupled to the output of said switching transistor, so that when power is applied to the control circuit, said load resistor is energized in response to the presence of the magnetic field.

8. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising:

at least one magnetic sensitive transistor having two collector terminals, and-controlled by the magnetic field of the electromagnetic control circuit;

at least one switching transistor, coupled in series with each collector of said magnetic transistor; and

a load resistor, connected to the output of said switching transistor so that said load resistor is energized in response to the presence of the magnetic field.

9. The contact free relay as recited in claim 8 comprising a permanent magnet, and means for positioning said permanent magnet with respect to said magnetic transistor.

10. The contact free relay as recited in claim 8 comprising at least one ferromagnetic yoke having an air gap for receiving said magnetic transistor, and a coil coupled to said yoke for magnetically energizing said yoke.

11. In a contact free relay, having an electromagnetic control circuit, including an electromagnetic coil and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contactfree elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improve-' ment comprising: t a ferromagnetic core comprising ferrite material, disposed within the magnetic field of the coil of the electromagnetic control circuit, and having an air gap provided in said core so that said core is divided into two separate ferromagnetic parts,.said air gap being disposed in said core at an angle of between 40 and with respect to the axis of the electromagnetic coil; and

at least one magnetic field dependent resistor, disposed within said air gap at an angle parallel to the angle at which said gap is disposed with respect to the axis of the coil. 

1. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising: at least two overlapping, longitudinally extending ferromagnetic yoke plates, disposed substantially in the center of the magnetic field, and coupled to the switching circuit; and at least two magnetic field dependent resistors, having an intermediate isolation layer, disposed between said pair of overlapping yoke plates.
 2. In a contact free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising: a first ferromagnetic yoke plate, extending longitudinally iN one direction, and disposed within the magnetic field; second and third yoke plates, overlapping said first yoke plate on each side, extending in an opposite direction, and disposed within the magnetic field; a first pair of magnetic field dependent resistors, disposed between said first yoke plate and said second yoke plate; and a second pair of magnetic field dependent resistors, disposed between said first yoke plate and said third yoke plate.
 3. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising: a first pair of spaced-apart, overlapping ferromagnetic yoke plates, extending in one direction, disposed in the magnetic field; a second pair of ferromagnetic yoke plates, alternately interdisposed with respect to said first pair of ferromagnetic plates, and extending in an opposite direction, disposed in the magnetic field; and a plurality of individual magnetic field dependent resistors, each disposed between said overlapping yoke plates.
 4. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising: a plurality of spaced-apart, overlapping magnetic field dependent resistors disposed within the magnetic field; and a plurality of ferromagnetic yoke plates, disposed between said overlapping resistors, overlapping each other, and extending from the center of the magnetic field in alternating, opposite directions.
 5. The contact free relay as recited in claim 4, comprising an additional plurality of corresponding pairs of magnetic field dependent resistors mounted side by side with respect to said ferromagnetic yoke plates, the width of said plates being expanded to accommodate said additional resistors.
 6. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising: a magnetic field dependent resistor, disposed within the magnetic field; ferromagnetic means, disposed within the magnetic field, on which said magnetic field resistor is disposed; a condenser, coupled across said magnetic field dependent resistor; a power supply; a variable resistor, coupled to the output of said power supply and to said magnetic field dependent resistor; a plurality of integrated, switching circuits coupled to said magnetic field dependent resistor; limit resistors, coupled to the output of said integrated switching circuits; and a plurality of switching transistors, coupled to the output of said limit resistors.
 7. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising: at least one magnetic sensitive transistor, having two collector terminals, controlled by the magnetic field of the electromagnetic control circuit; an adjustable voltage divider, coupled to the base of said magnetic sensitive transistor; a first resistor, coupled to each of said magnetic transistor collectors, for coupling power to said magnetic transistor; a second resistor, coupLed to one of said collectors of said magnetic transistors; at least one switching transistor, having its base coupled in series to said second resistor; and a load resistor, coupled to the output of said switching transistor, so that when power is applied to the control circuit, said load resistor is energized in response to the presence of the magnetic field.
 8. In a contact-free relay, having an electromagnetic control circuit and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising: at least one magnetic sensitive transistor having two collector terminals, and controlled by the magnetic field of the electromagnetic control circuit; at least one switching transistor, coupled in series with each collector of said magnetic transistor; and a load resistor, connected to the output of said switching transistor so that said load resistor is energized in response to the presence of the magnetic field.
 9. The contact free relay as recited in claim 8 comprising a permanent magnet, and means for positioning said permanent magnet with respect to said magnetic transistor.
 10. The contact free relay as recited in claim 8 comprising at least one ferromagnetic yoke having an air gap for receiving said magnetic transistor, and a coil coupled to said yoke for magnetically energizing said yoke.
 11. In a contact free relay, having an electromagnetic control circuit, including an electromagnetic coil and at least one electronic switching circuit disposed within the magnetic field of the electromagnetic control circuit, and including contact-free elements controlled by the magnetic field and connected with at least one controllable semiconductor, the improvement comprising: a ferromagnetic core comprising ferrite material, disposed within the magnetic field of the coil of the electromagnetic control circuit, and having an air gap provided in said core so that said core is divided into two separate ferromagnetic parts, said air gap being disposed in said core at an angle of between 40* and 90* with respect to the axis of the electromagnetic coil; and at least one magnetic field dependent resistor, disposed within said air gap at an angle parallel to the angle at which said gap is disposed with respect to the axis of the coil. 